The diaphragm is a large flat muscle that divides the chest and abdomen. Various conditions that affect the diaphragm may be identified on SPECT MPI raw projection image data (Table 16.1). The position of the hemidiaphragms should be noted during review. The left hemidiaphragm is a common vexing source of artifact on the reconstructed SPECT images.

When fluid is present on both sides of the diaphragm (as in pleural effusion with ascites), the hemidiaphragm(s) may be visualized as a soft-tissue structure outlined by surrounding “cold” fluid (Fig. 16.1). A high right hemidiaphragm may lead to a processing artifact when the liver is “hot” and adjacent to the heart (Burrell and MacDonald 2006). Normally, the dome of the liver has a smooth and curvilinear margin; surgical changes to the right hemidiaphragm may result in an irregular contour at the dome of the liver (Fig. 16.2). A high left hemidiaphragm may have “hot” stomach or small intestine, or even spleen or large intestine, immediately subjacent to it, leading to well-known problematic “hot” and/or “cold” processing artifacts in the inferior and inferior-lateral myocardium (Pitman et al. 2005). Eventration of the left hemidiaphragm leads to elevation into the chest with displacement of abdominal contents alongside the heart (see Fig. 22.​5). Diaphragmatic hernias contain abdominal contents, including the stomach and small intestine (Chamarthy and Travin 2010; Gedik et al. 2007).